Multi step transmission

ABSTRACT

A multi-stage transmission comprising planetary gear sets (P 1 , P 2 , P 3 , P 4 ), shafts, and shift elements. The sun gear of gearset (P 1 ) couples housing (G), the carrier of gearset (P 1 ) couples shaft ( 3 ) which couples housing (G), via brake ( 03 ), and shaft ( 1 ) via clutch ( 13 ) and shaft ( 5 ) via clutch ( 35 ). Shaft ( 5 ) couples the ring gear of gearset (P 2 ) and the sun gears of gearsets (P 3 , P 4 ). Shaft ( 1 ) couples the sun gear of gearset (P 2 ) and the carrier of gearset (P 3 ). Shaft ( 6 ) couples the carrier of gearset (P 2 ) and the ring gear of gearset (P 1 ), the ring gear of set (P 4 ) couples shaft ( 4 ) which couples housing (G) via brake ( 04 ), and output shaft ( 2 ) couples the carrier of gearset (P 4 ) and shaft ( 7 ), which couples, via clutch ( 27 ), the ring gear of gearset (P 3 ).

This application claims priority from German patent application serialno. 10 2009 028 705.1 filed Aug. 20, 2009.

FIELD OF THE INVENTION

The present invention relates to a multi step transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, andtypically are connected to a start-up element, such as a hydrodynamictorque converter or a fluid coupling, that is subject to a slip effectand is provided optionally with a lock-up clutch.

Such an automatic transmission is known, for example, from theapplicant's DE 199 49 507 A1, according to which two non-shiftablefront-mounted gear sets are provided on the drive shaft and generate tworotational speeds on the output side, which, in addition to therotational speed of the drive shaft, can be selectively meshed with ashiftable double planetary gear set acting on the output shaft byselective engagement of the shift elements such that only one of the twocurrently actuated shift elements must be engaged or disengaged to shiftfrom one gear to the next higher or lower gear.

By using five shift elements, seven forward gears are obtained; by usingsix shift elements, nine or ten forward gears are obtained.

Furthermore, DE 102 13 820 A1 makes known a multi-speed automatictransmission with eight forward gears and one reverse gear, whichcomprises a first input path T1 of a first transmission ratio; an inputpath T2 that has a higher transmission ratio than that of input path T1;a Ravigneaux type planetary gear set with four elements, namely, a firstelement, a second element, a third element and a fourth element in thesequence of elements in a rotational speed diagram; a clutch C-2, whichtransfers rotation of the input path T2 to the first element S3; aclutch C-1, which transfers rotation from the input path T2 to thefourth element S2; a clutch C-4, which transfers rotation from the inputpath T1 to the first element; a clutch C-3, which transfers rotationfrom the input path T1 to the second element C3; a brake B-1, whichproduces meshing of the fourth element; a brake B-2, which producesmeshing of the second element; and an output element that is coupled tothe third element S3.

Furthermore, a nine-speed multi step transmission is known from DE 29 36969 A1; it comprises eight shift elements and four gear sets, whereinone gear set serves as a front-mounted gear set and the main gearingincludes a Simpson set and a further gear set serving as reversegearing.

Further multi step transmissions are known, for example, from theapplicant's DE 102005010210 A1 and DE 102006006637 A1.

Automatically shiftable vehicle transmissions, of a planetary design,are already generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a low number of shift elements, and minimize the need fordouble shifting when sequential shifting is performed, thereby ensuringthat only one shift element is ever switched when shifting is performedin defined groups of gears.

The applicant's document, DE 102008000428.3, which is not yet published,discloses a multi step transmission of a planetary design that includesan input shaft and an output shaft which are disposed in a housing. Theknown transmission includes at least four planetary gear sets, which aredesignated, in the following, as the first, second, third, and fourthplanetary gear set, at least eight rotatable shafts which are designatedin the following as the drive shaft, output shaft, third, fourth, fifth,sixth, seventh, and eighth shaft, and at least six shift elementscomprising brakes and clutches, whose selected engagement producesdifferent transmission ratios between the input shaft and the outputshaft such that preferably nine forward gears and one reverse gear canbe realized.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, form a shiftable front-mounted gear set,wherein the third and fourth planetary gear sets form a main gear set.

In the known multi step transmission, the carriers of the first andsecond planetary gear sets are coupled together via the fourth shaft,which is connected to an element of the main gear set, the ring gear ofthe first planetary gear set is coupled to the sun gear of the secondplanetary gear set via the eighth shaft, which is detachably connectableto the drive shaft via the first clutch, and the sun gear of the firstplanetary gear set can be coupled to a housing of the transmission bymeans of the third shaft, via a first brake, and is detachablyconnectable to the drive shaft via a second clutch, the ring gear of thesecond planetary gear set can be coupled to a housing of thetransmission by means of the fifth shaft via a second brake. Inaddition, the seventh shaft is constantly connected to at least oneelement of the main gear set, and can be coupled to a housing of thetransmission via a third brake, the sixth shaft is constantly connectedto at least one further element of the main gear set and is detachablyconnectable to the drive shaft, via a third clutch; the output shaft isconstantly connected at least to one further element of the main gearset.

In the known transmission, the fourth shaft is preferably constantlyconnected to the ring gear of the third planetary gear set, the sixthshaft is constantly connected to the ring gear of the fourth planetarygear set and to the carrier of the third planetary gear set, and isdetachably connectable to the drive shaft via the third clutch.Furthermore, the seventh shaft is constantly connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to ahousing of the transmission via the third brake. In this case, theoutput drive is produced via the output shaft that is constantlyconnected to the carrier of the fourth planetary gear set. Furthermore,the third and fourth planetary gear sets can be combined or reduced to aRavigneaux set having a common carrier and a common ring gear.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a multi steptransmission of the initially described type, which has nine forwardgears and at least one reverse gear having a sufficient transmissionratio, in which the design complexity and the overall size, inparticular the overall length and the weight, are optimized, and inwhich efficiency is improved with respect to drag losses and gearinglosses. In addition, in the multi step transmission according to theinvention, minimal support moments should act on the shift elements. Thetransmission, according to the invention, should be particularly suitedfor a front transverse installation.

Accordingly, a multi step transmission, according to the invention, of aplanetary design is proposed which has an input shaft and an outputshaft which are disposed in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and at least six shift elements comprising brakes andclutches, whose selected engagement produces different transmissionratios between the drive shaft and the output shaft, and thereforepreferably nine forward gears and one reverse gear can be realized.

The planetary gear sets, viewed axially, are disposed in the sequence offirst planetary gear set, second planetary gear set, third planetarygear set, fourth planetary gear set, and are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is fixed, the ring gear hasa direction of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablysupported, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, wherein each inner planetgear meshes with only one outer planet gear. As a result, when thecarrier is fixed, the ring gear has the same direction of rotation asthe sun gear.

According to the invention, the sun gear of the first planetary gear setis coupled to a housing of the transmission, the carrier of the firstplanetary gear set is connected to the third shaft which can be coupledto a housing of the transmission via a second brake, is detachablyconnectable to the drive shaft via a first clutch and to the fifth shaftvia second clutch, the fifth shaft is connected to the ring gear of thesecond planetary gear set, to the sun gear of the third planetary gearset and to the sun gear of the fourth planetary gear set, and the driveshaft is connected to the carrier of the third planetary gear set, andis operatively connected to the sun gear of the second planetary gearset.

Furthermore, the ring gear of the first planetary gear set is connectedto the sixth shaft, which is operatively connected to the carrier of thesecond planetary gear set, the ring gear of the fourth planetary gearset can be coupled to a housing of the transmission via a first brake,and the output shaft is detachably connectable, via a third shaft, tothe seventh shaft that is connected to the ring gear of the thirdplanetary gear set, and is connected to the carrier of the fourthplanetary gear set.

Preferably, the drive shaft is detachably connectable to the sun gear ofthe second planetary gear set via an eighth shaft, which is connected tothe sun gear of the second planetary gear set, and via a fourth clutchdetachably connecting the eighth shaft to the drive shaft, and the sixthshaft is directly connected to the carrier gear of the second planetarygear set.

According to a further embodiment of the invention it is provided thatthe drive shaft is directly connected to the sun gear of the secondplanetary gear set, the sixth shaft is not directly connected to thecarrier of the second planetary gear set, but rather is detachablyconnectable via a further shaft, which is connected to the carrier ofthe second planetary gear set, and via a further clutch detachablyconnecting the further shaft to the sixth shaft.

The embodiment of the multi step transmission, according to theinvention, results in transmission ratios that are particularly suitablefor passenger vehicles, and in a greater overall gear ratio of the multistep transmission, thereby improving driving smoothness andsignificantly reducing fuel consumption.

Furthermore, the design complexity is significantly reduced with themulti step transmission, according to the invention, due to a low numberof shift elements. Using the multi step transmission according to theinvention, it is advantageously possible to perform a start-up using ahydrodynamic converter, an external start-up clutch, or any othersuitable external start-up element. It is also conceivable to perform astart-up using a start-up element integrated in the transmission.Preferably, a shift element that is actuated in the first forward gearand in the reverse gear is suitable.

Moreover, the multi step transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Furthermore, low moments are present in the shift elements and in theplanetary gear sets of the multi step transmission, therebyadvantageously reducing wear in the multi step transmission. Inaddition, the low moments make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following, as anexample, with reference to the attached figures. They show:

FIG. 1: a schematic view of a first preferred embodiment of a multi steptransmission according to the invention;

FIG. 2: a schematic view of a second preferred embodiment of a multistep transmission according to the invention; and

FIG. 3: an example of a shift pattern for a multi step transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi step transmission, according to the invention,which has a drive shaft 1, an output shaft 2, and four planetary gearsets P1, P2, P3 and P4 which are disposed in a housing G. Planetary gearsets P1, P2, P3 and P4, in the example shown in FIG. 1, are designed asminus planetary gear sets. According to the invention, at least oneplanetary gear set can be implemented as a plus planetary gear set ifthe carrier and ring gear connection are exchanged and, simultaneously,the value of the stationary transmission ratio is increased by 1 incomparison to the embodiment as a minus planetary gear set.

In the embodiment shown, the planetary gear sets, viewed axially, aredisposed in the sequence P1, P2, P3 and P4.

As shown in FIG. 1, six shift elements are provided, namely, two brakes,03, 04, and four clutches 13, 35, 18 and 27. The spatial disposition ofthe shift elements can be arbitrary, and is limited only by thedimensions of the outer design. The clutches and the brakes of thetransmission are preferably implemented as friction shift elements orlamellar shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi step transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft isthe first shaft, and the output shaft is the second shaft of thetransmission.

According to the invention, in the multi step transmission according toFIG. 1, the sun gear of the first planetary gear set P1 is coupled to ahousing G of the transmission (shaft 0), the carrier of the firstplanetary gear set P1 is connected to the third shaft 3, which can becoupled to a housing G of the transmission via a second brake 03, to thedrive shaft 1 via a first clutch 13, and can be detachably connected tothe fifth shaft 5 via a second clutch 35.

As shown in FIG. 1, the fifth shaft 5 is connected to the ring gear ofthe second planetary gear set P2, to the sun gear of the third planetarygear set P3 and to the sun gear of the fourth planetary gear set P4. Thedrive shaft 1 is connected to the carrier of the third planetary gearset P3. The eighth shaft 8 is connected to the sun gear of the secondplanetary gear set P2. A fourth clutch 18, detachably connects theeighth shaft 8 to the drive shaft 1. Via the eighth shaft 8 and thefourth clutch 18, the drive shaft 1 can be detachably connected to thesun gear of the second planetary gear set P2.

According to the invention, the ring gear of the first planetary gearset P1 is connected to the sixth shaft 6, which is directly connected tothe carrier of the second planetary gear set P2, the ring gear of thefourth planetary gear set P4 is connected to the fourth shaft 4, whichcan be coupled to a housing G of the transmission via a first brake 04;the output shaft 2 can be detachably connected via a third clutch 27 tothe seventh shaft 7, which is connected to the ring gear of the thirdplanetary gear set P3, and is connected to the carrier of the fourthplanetary gear set P4.

According to the invention, the first clutch 13 and the fourth clutch18, viewed axially, can be disposed between the first and the secondplanetary gear sets P1, P2, wherein the third clutch 27, viewed axially,can be disposed between the third and fourth planetary gear sets P3, P4.

Furthermore, the second brake 03 and the second clutch 35, viewedaxially, are preferably disposed next to each other.

The embodiment shown in FIG. 2 differs from the embodiment according toFIG. 1 in that the detachable connection of the drive shaft 1 to the sungear of the second planetary gear set P2 via the fourth clutch 18, whichdetachably connects the drive shaft 1 to the eighth shaft 8, and via theeighth shaft 8 which is connected to the sun gear of the secondplanetary gear set P2, is replaced by a direct connection of the driveshaft 1 to the sun gear of the second planetary gear set P2, wherein inthis case, the sixth shaft 6 cannot be connected directly to the carrierof the second planetary gear set P2, but rather via a further shaft 8′,which is connected to the carrier of the second planetary gear set P2,and via a further clutch 68, which detachably connects further shaft 8′to the sixth shaft 6.

FIG. 3 shows an example of a shift pattern of a multi step transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift pattern shows, as examples, the particular transmission ratiosi of the individual gear steps, and, to be determined therefrom, thegear increments or step changes phi to the next higher gear, wherein thevalue 9.005 is the transmission ratio spread.

Typical values for the stationary transmission ratios of the planetarygear sets P1, P2, P3 and P4 implemented as minus planetary gear sets are−3.90, −1.60, −2.201 and −2.103, respectively. FIG. 3 shows that doubleshifting or group shifting is avoided when shifting sequentially sincetwo adjacent gear steps share two shift elements. It is also shown thata large transmission ratio spread is attained with small gearincrements.

The first forward gear is attained by engaging the first brake 04 andthe second and fourth clutches 35, 18; the second forward gear isattained by engaging the first brake 04 and the first and secondclutches 13, 35; the third forward gear is attained by engaging thefirst brake 04 and the first and fourth clutches 13, 18; the fourthforward gear is attained by engaging the first brake 04 and the thirdand fourth clutches 27, 18; the fifth forward gear is attained byengaging the first, third and fourth clutches 13, 27, 18; the sixthforward gear, which is preferably implemented as a direct gear, isimplemented by engaging the first, second, and third clutches 13, 35,27; the seventh forward gear is attained by engaging the second, thirdand fourth clutches 35, 27, 18; the eight forward gear is attained byengaging the second brake 03 and the second and third clutches 35, 27;and the ninth forward gear is attained by engaging the second brake 03and the third and fourth clutch 27, 18, and the reverse gear is attainedby engaging the first and second brakes 04, 03 and the fourth clutch 18.

Since the first brake 04 and the fourth clutch 18 are engaged in thefirst forward gear and in the first reverse gear, these shift elementscan be used as start-up elements.

For the case in which, according to the embodiment depicted in FIG. 2,the fourth clutch 18 is omitted and is replaced by the further clutch68, i.e., for the case in which the drive shaft 1 is directly connectedto the sun gear of the second planetary gear set P2 instead ofdetachably connectable to the sun gear of the second planetary gear setP2 via the eighth shaft 8 and the fourth clutch 18, and the sixth shaft6 is not directly connected to the carrier of the second planetary gearset P2, but instead via a further shaft 8′, which is connected to thecarrier of the second planetary gear set P2, and via a clutch 68, whichdetachably connects the further shaft 8′ to the sixth shaft 6, so thatthe fourth clutch 18 is replaced by the further clutch 68 in the shiftpattern shown in FIG. 3.

According to the invention, different gear increments can also resultfrom the same gear pattern depending on the shift logic, thereby makingit possible to realize an application-specific or vehicle-specificvariation.

According to the invention, it is possible to provide additionalfreewheels at each suitable location of the multi stepped transmission,for example, between a shaft and the housing, or possibly to connect twoshafts.

According to the invention, an axle differential and/or a distributordifferential can be disposed on the drive side or on the output side.

Within the scope of an advantageous development, the drive shaft 1 canbe separated from a drive motor, as needed, by a clutch element, whereina hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, awet start-up clutch, a magnetic powder clutch, or a centrifugal clutchcan be used as the clutch element. It is also possible to dispose such astart-up element in the power flow direction after the transmissionwherein, in this case, the drive shaft 1 is continuously connected tothe crankshaft of the engine.

The multi step transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the engine andthe transmission.

Within the scope of a further, not represented embodiment of theinvention, a wear-free brake, for instance, a hydraulic or electricretarder or the like, can be disposed on each shaft, preferably on thedrive shaft 1 or the output shaft 2, which is of special significancefor use in commercial vehicles in particular. Furthermore, a powertake-off drive can be provided on each shaft, preferably on the driveshaft 1 or the output shaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi step transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

Obviously, any structural embodiment, in particular any spatialdisposition of the planetary gear sets and the shift elementsindividually and relative to each other, and insofar as it istechnically expedient, falls under the scope of protection of thepresent claims, without influencing the function of the transmission asspecified in the claims, even if these embodiments are not explicitlyrepresented in the figures or in the description.

REFERENCE CHARACTERS

-   0 Shaft-   1 First shaft, drive shaft-   2 Second shaft, output shaft-   3 Third shaft-   4 Fourth shaft-   5 Fifth shaft-   6 Sixth shaft-   7 Seventh shaft-   8 Eighth shaft-   8′ Further shaft-   03 Second brake-   04 First brake-   13 First clutch-   18 Fourth clutch-   27 Third clutch-   35 Second clutch-   68 Further clutch-   P1 First planetary gear set-   P2 Second planetary gear set-   P3 Third planetary gear set-   P4 Fourth planetary gear set-   i Transmission ratio-   phi Step change-   G Housing

1. A multi step transmission of a planetary design for an automatictransmission for a motor vehicle, the multi step transmissioncomprising: a drive shaft (1); an output shaft (2); first, second, thirdand fourth planetary gear sets (P1, P2, P3, P4) which are disposed in atransmission housing (G), each of the first, the second, the third, andthe fourth planetary gear sets (P1, P2, P3, P4) comprising a sun gear, acarrier and a ring gear; a third rotatable shaft (3), a fourth rotatableshaft (4), a fifth rotatable shaft (5), a sixth rotatable shaft (6), aseventh rotatable shaft (7), and an eighth rotatable shaft (8, 8′); atleast six shift elements (03, 04, 13, 18, 27, 35, 68) comprising a firstbrake (04), a second brake (03), a first clutch (13), a second clutch(35), a third clutch (27), and a fourth clutch (18, 68) whose selectedengagement produces different transmission ratios between the driveshaft (1) and the output shaft (2) such that nine forward gears and onereverse gear can be achieved; wherein the sun gear of the firstplanetary gear set (P1) is connected to the housing (G); the carrier ofthe first planetary gear set (P1) is directly connected to the thirdshaft (3) which is connectable to the housing (G) via the second brake(03); the third shaft (3) is directly connected to the first clutch(13), and the first clutch (13) is directly connected to the drive shaft(1), whereby the carrier of the first planetary gear set (P1) isdetachably connectable to the drive shaft (1), via the first clutch(13); the third shaft (3) is directly connected to the second clutch(35), and the second clutch (35) is directly connected to the fifthshaft (5), whereby the third shaft (3) is detachably connectable to thefifth shaft (5), via the second clutch (35); the fifth shaft (5) isconnected to the ring, gear of the second planetary gear set (P2), thesun gear of the third planetary gear set (P3) and the sun gear of thefourth planetary gear set (P4); the drive shaft (1) is operativelyconnected to the sun gear of the second planetary gear set (P2) and isconnected to the carrier of the third planetary gear set (P3); the sixthshaft (6) is connected to the ring gear of the first planetary gear set(P1) and is operatively connected to the carrier of the second planetarygear set (P2); the ring gear of the fourth planetary gear set (P4) isconnected to the fourth shaft (4) which is connectable to the housing(G) via the first brake (04); and the output shaft (2) is connected tothe carrier of the fourth planetary gear set (P4) and is detachablyconnected to the seventh shaft (7), via the third clutch (27), and theseventh shaft (7) is connected to the ring gear of the third planetarygear set (P3).
 2. The multi-stage transmission according to claim 1,wherein the eighth shaft (8) is connected to the sun gear of the secondplanetary gear set (P2), and the drive shaft (1) is detachablyconnectable to the eighth shaft (8) and the sun gear of the secondplanetary gear set (P2) via the fourth clutch (18), and the sixth shaft(6) is directly connected to the carrier of the second planetary gearset (P2).
 3. The multi-stage transmission according to claim 2, whereina first forward gear is achieved by engagement of the first brake (04)and the second and the fourth clutches (35, 18); a second forward gearis achieved by engagement of the first brake (04) and the first and thesecond clutches (13, 35); a third forward gear is achieved by engagementof the first brake (04) and the first and the fourth clutches (13, 18);a fourth forward gear is achieved by engagement of the first brake (04)and the third and the fourth clutches (27, 18); a fifth forward gear isachieved by engagement of the first, the third and the fourth clutches(13, 27, 18); a sixth forward gear is achieved by engagement of thefirst, the second and the third clutches (13, 35, 27); a seventh forwardgear is achieved by engagement of the second, the third and the fourthclutches (35, 27, 18); an eighth forward gear is achieved by engagementof the second brake (03) and the second and the third clutches (35, 27);a ninth forward gear is achieved by engagement of the second brake (03)and the third and the fourth clutches (27, 18); and the reverse gear isachieved by engagement of the first and the second brakes (04, 03) andthe fourth clutch (18).
 4. The multi step transmission according toclaim 1, wherein the first, the second, the third and the fourthplanetary gear sets (P1, P2, P3, P4) are minus planetary gear sets.
 5. Amulti step transmission of a planetary design for an automatictransmission for a motor vehicle, the multi step transmissioncomprising: a drive shaft (1); an output shaft (2); first, second, thirdand fourth planetary gear sets (P1, P2, P3, P4) which are disposed in atransmission housing (G), each of the first, the second, the third, andthe fourth planetary gear sets (P1, P2, P3, P4) comprising a sun gear, acarrier and a ring gear; a third rotatable shaft (3), a fourth rotatableshaft (4), a fifth rotatable shaft (5), a sixth rotatable shaft (6), aseventh rotatable shaft (7), and an eighth rotatable shaft (8, 8′); atleast six shift elements (03, 04, 13, 18, 27, 35, 68) comprising a firstbrake (04), a second brake (03), a first clutch (13), a second clutch(35), a third clutch (27), and a fourth clutch (18, 68) whose selectedengagement produces different transmission ratios between the driveshaft (1) and the output shaft (2) such that nine forward gears and onereverse gear can be achieved; wherein the sun gear of the firstplanetary gear set (P1) is connected to the housing (G); the carrier ofthe first planetary gear set (P1) is connected to the third shaft (3)which is connectable to the housing (G) via the second brake (03), andthe carrier of the first planetary gear set (P1) is detachablyconnectable to the drive shaft (1), via the first clutch (13), and tothe fifth shaft (5), via the second clutch (35); the fifth shaft (5) isconnected to the ring gear of the second planetary gear set (P2), thesun gear of the third planetary gear set (P3) and the sun gear of thefourth planetary gear set (P4); the drive shaft (1) is operativelyconnected to the sun gear of the second planetary gear set (P2) and isconnected to the carrier of the third planetary gear set (P3); the sixthshaft (6) is connected to the ring gear of the first planetary gear set(P1) and is operatively connected to the carrier of the second planetarygear set (P2); the ring gear of the fourth planetary gear set (P4) isconnected to the fourth shaft (4) which is connectable to the housing(G) via the first brake (04); and the output shaft (2) is connected tothe carrier of the fourth planetary gear set (P4) and is detachablyconnected to the seventh shaft (7), via the third clutch (27), and theseventh shaft (7) is connected to the ring gear of the third planetarygear set (P3); the drive shaft (1) is directly connected to the sun gearof the second planetary gear set (P2), and the eighth shaft (8′) isconnected to the carrier of the second planetary gear set (P2), and thesixth shaft (6) is detachably connectable to the eighth shaft (8′) andthe carrier of the second planetary gear set (P2) via the fourth clutch(68).
 6. The multi-stage transmission according to claim 5, wherein afirst forward gear is achieved by engagement of the first brake (04) andthe second and the fourth clutches (35, 18); a second forward gear isachieved by engagement of the first brake (04) and the first and thesecond clutches (13, 35); a third forward gear is achieved by engagementof the first brake (04) and the first and the fourth clutches (13, 18);a fourth forward gear is achieved by engagement of the first brake (04)and the third and the fourth clutches (27, 18); a fifth forward gear isachieved by engagement of the first, the third and the fourth clutches(13, 27, 18); a sixth forward gear is achieved by engagement of thefirst, the second and the third clutches (13, 35, 27); a seventh forwardgear is achieved by engagement of the second, the third and the fourthclutches (35, 27, 18); an eighth forward gear is achieved by engagementof the second brake (03) and the second and the third clutches (35, 27);a ninth forward gear is achieved by engagement of the second brake (03)and the third and the fourth clutches (27, 18); and the reverse gear isachieved by engagement of the first and the second brakes (04, 03) andthe fourth clutch (18).